This invention relates to high efficiency lasers, and particularly to miniature lasers having a visible beam.
Lasers generally have a rather low efficiency, being the ratio of input energy to output energy; commercially available ruby lasers typically have an efficiency of less than 1%. Nevertheless, low efficiency is accepted because laser beams have a very high energy density.
Low efficiency is associated with several problems. Firstly the power source must be relatively large for a given energy output which can lead to rather bulky equipment having a large mass; such equipment is not suitable for use in portable or light weight applications, or in cases where small size is essential. Secondly a very large heat sink must be provided to remove waste heat for otherwise the laser may be damaged; such a heat sink further increases the bulk, mass and complication of laser devices, and in many cases comprises a water cooling arrangement having pipes, valves and the like which further restrict portability and flexibility of use. These problems also add to the cost of lasers and have hitherto restricted their application considerably.
Laser light has a generally normal distribution of frequencies, and within the frequency range a number of modes may be encountered. This is because there are usually several resonances between the reflector faces of the laser, each resonance being at a different frequency. It may be desirable to obtain a laser output at any one of these frequencies and thus anti-reflection and reflection coatings have been developed in order that only light at the desired frequency (the desired mode) is permitted to reflect between the laser end faces.